Researchers study salt's potential to store energy

Jun 02, 2009 by Renee Meiller

(PhysOrg.com) -- When the wind blows, it blows — sometimes to a fault. The same is true for the sun: It can beat down relentlessly, scorching everything — and everyone-beneath its intense rays.

Yet, like the flip of a light switch, the breeze stills and the sun slips under the clouds, often for days.

This unpredictability is, perhaps, the greatest barrier in researchers' quest to integrate wind and solar as mainstream energy-generation technologies. "The current administration, I think, has properly characterized that , in some fashion, whether it be with batteries, thermal storage or some new technologies, is the only way to get renewables to grow, because they're fundamentally an intermittent energy source," says Michael Corradini, a University of Wisconsin-Madison professor of engineering physics.

At UW-Madison, researchers see potential for storing heat in a mineral found on kitchen counters and restaurant tables worldwide.

They're studying salt.

Heated to temperatures sometimes far exceeding 1,500 degrees Fahrenheit, salt liquefies. Despite this red-hot temperature, molten salt can act as both a coolant and as an agent for storing heat.

"Molten salts have many advantages," says Kumar Sridharan, UW-Madison distinguished research professor of engineering physics. "Why they have these great heat-storage and heat-transfer capabilities is that they have very good conductivity, they have good specific heat and high density — compared to gases, at least — and those are the properties that dictate how a given volume of material will hold heat or transfer heat from one location to another. So it has all these attractive properties."

As a result, salts could gain a foothold in applications ranging from concentrating solar towers and nuclear reactors to oil recovery and biomass breakdown.

"It's just been in the recent few years that people have really started looking at the salts again for a bunch of these applications, and starting to look at different combinations of ternary and binary — and even multiple constituents of the salts — for different advantages," says Mark Anderson, a UW-Madison engineering physics senior scientist.

Anderson, Sridharan and Todd Allen, a UW-Madison engineering physics assistant professor, have been studying molten salt for about five years. Their research, which stretches into three separate laboratories, includes experiments to measure salt heat-transfer properties, determine the best salt mixtures for different applications, and develop materials and coatings able to withstand salt corrosion at extremely high temperatures.

Similar to table salt, molten salt starts as pea-sized granules. The researchers are working with a salt that melts at around 220 degrees Fahrenheit, and one goal is to find salts that melt at low temperatures, but are still stable up to very high temperatures. "It seems weird to talk about something that melts at 212 degrees Fahrenheit as a coolant, but a reactor and a solar energy system can operate more efficiently at 1,600 degrees Fahrenheit, so a melting point of 212 degrees Fahrenheit is still low compared to that," says Anderson.

Applied to solar-energy towers, molten salt in the collector heats up as sunlight focuses on it. An exchanger converts heat in the salt into steam or a high-temperature gas, which spins a turbine for generating electricity. In nuclear energy, liquid salts are more versatile, acting as a coolant to strip heat from the fuel and generate electricity or serve as an environmentally friendly form of high-temperature process heat for chemical and industrial products. In addition, molten salt is useful in an electrochemical process for separating nuclear waste, enabling nuclear power plants to recycle fuel components.

For oil extraction, some companies are studying the feasibility of more environmentally friendly in-ground refineries, where they could use the heat in molten salt from a power plant to super-heat the earth around oil shale. "They can actually heat up the oil shale and try to remove the valuable petroleum products deep in the ground, without having to disrupt the surface by digging down and processing the oil shale above ground," says Anderson.

The researchers also are studying how high-temperature sodium chloride can break down biomass to form syngas, a synthetic natural gas that forms the basis for bio-petroleum products. "The biomass would be used for alternative energy," he says. "So instead of oil, you make biogas, biodiesel."

Anderson and Sridharan say molten salt can help alternative-energy sources grow. "I think it's going to increase in popularity," says Anderson. "And we have to understand the materials, we have to understand the heat transfer properties and we have to understand how the chemistry works. And once we understand that, I think it's going to take off and be used in a lot of different energy applications."

Provided by University of Wisconsin-Madison (news : web)

Explore further: Refocusing research into high-temperature superconductors

add to favorites email to friend print save as pdf

Related Stories

Salt could cool cores of advanced nuclear reactors

Nov 03, 2006

The water in a conventional nuclear reactor cools the core, but a graduate student at the University of Missouri-Rolla says salt would be a better alternative in some advanced reactor designs.

Engineer creates a new tool for keeping computers cool

Jul 11, 2005

Anyone who has listened to the constant whir of a computer's fan or held a laptop for too long knows how blazing hot computers can get. In fact, today's ultra-powerful computers generate so much heat that air cooling tec ...

The Dynamo in the Cornfield

Jan 05, 2005

To understand our planet's magnetic field, Wisconsin scientists are studying a ball of molten metal In an underground bunker that brushes up against a barnyard on one side and a cornfield on the other, scienti ...

Solar Cells with 60% Efficiency?

Jan 09, 2008

Nuclear Engineer Lonnie Johnson, best known for his invention of the super soaker squirt gun, has recently designed a new type of solar energy technology that he says can achieve a conversion efficiency rate ...

A hot idea for insulating tiny batteries

Jan 10, 2007

Engineering physics researchers are devising a unique "blanket" that will enable them to squeeze as much electricity as possible from nuclear-powered batteries the size of a grain of coarse salt.

Recommended for you

Refocusing research into high-temperature superconductors

13 hours ago

Below a specific transition temperature superconductors transmit electrical current nearly loss-free. For the best of the so-called high-temperature superconductors, this temperature lies around -180 °C – a temperature ...

MRI for a quantum simulation

19 hours ago

Magnetic resonance imaging (MRI), which is the medical application of nuclear magnetic resonance spectroscopy, is a powerful diagnostic tool. MRI works by resonantly exciting hydrogen atoms and measuring ...

50-foot-wide Muon g-2 electromagnet installed at Fermilab

19 hours ago

One year ago, the 50-foot-wide Muon g-2 electromagnet arrived at the U.S. Department of Energy's Fermi National Accelerator Laboratory in Illinois after traveling 3,200 miles over land and sea from Long Island, ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

jerryd
not rated yet Jun 07, 2009

I agree we need much better understanding of salts. Another thing we need are small steam/Rankine engines of 3-10hp for home RE systems to take advantage of salts in home, small business settings.